1. Field of the Invention
The present invention relates to a device for protecting internal devices of a laser beam printer (LBP) against heat emitted from a fixing device in a laser beam printer (LBP), and in particular, to a device for discharging fixing heat from the fixing device to the outside of a laser beam printer (LBP) to prevent heat transfer from a fixing device to other internal devices of the laser beam printer (LBP).
2. Description of the Related Art
A laser beam printer (LBP) exemplary of contemporary practice in the art includes a paper feeder for feeding a sheet of paper, a developing device for forming an image onto the paper sheet fed from the paper feeder, a fixing device for fixing the image on the paper sheet, and a discharging device for discharging the paper having thereon the fixed image. The paper feeder includes a pick-up roller located at an appropriate position of a printer body, for feeding a plurality of paper sheets loaded on a paper cassette, sheet by sheet, and a register roller for aligning the leading end of a paper sheet fed by the pick-up roller.
In the developing device, an organic photoconductive (OPC) drum is rotatably installed to produce an electrostatic latent image corresponding to a digital image signal received from a laser scanner located in the body of the laser beam printer (LBP). In contact with the organic photoconductive (OPC) drum are a charge roller for charging the organic photoconductive (OPC) drum with a high voltage before exposure, a transfer roller for forming an image on a paper sheet, and a developing roller for developing the electrostatic latent image to form a toner image on the organic photoconductive (OPC) drum. A supply roller rotates in contact with the developing roller, for supplying toner from a toner hopper to the developing roller. The toner is frictionally charged by rotating the developing roller and the supply roller in the same direction and is supplied to the developing roller. A doctor blade is located above the developing roller with an end thereof fixed to a frame and the other end thereof directed downward to be in contact with the developing roller, for regulating the thickness of a toner layer coated on the developing roller.
In the fixing device, a pressure roller and a heat roller are rotated in contact with each other, respectively to fix a toner image on the paper sheet with a predetermined pressing force and melt toner particles on the paper sheet. The heat roller includes a heat lamp to fix the toner image at about 180.degree. C.
A body frame and other internal devices of the laser beam printer (LBP) as described above are susceptible to damage due to a high temperature around the fixing device. In particular, when an excess of the heat is transferred to the developing unit, the toner powder is likely to be melted into a liquid or hardened. To overcome these problems, a ventilation fan is installed in a ventilation hole on a side surface of the body frame over the fixing device, to exhaust heated air stagnated in the fixing device to the outside or cool the fixing device. However, since the fixing device should be maintained at a specified temperature once the laser beam printer (LBP) has turned on, even if a printing operation is not performed, the ventilation fan should continue its action. As a result, power consumption is increased and the operational noise of the ventilation fan is generated.
U.S. Pat. No. 4,427,285 to Stange entitled Direct Duplex Printing On Pre-Cut Copy Sheets, discloses a two photoreceptor, single pass duplex reproduction system having a heat insulating prefuser transport device and first and second transfer stations. In particular, the prefuser transport is a pair of cold, toner compacting rolls adjacent the second transfer station for immediate pick up of a copy sheet supporting unfused images on both sides. The compacting rolls tack the unfused images to the copy sheet. It is disclosed the compacting rolls also insulate the photoreceptor from the heat of the fuser and convey the copy sheet immediately to the fuser. The fuser permanently fixes the images onto the copy sheet in one fuser operation.
U.S. Pat. No. 4,847,636 to Durbeck, et al. entitled Thermal Drop-On-Demand Ink Jet Print Head, disclose a thermal drop-on-demand ink jet print head in which thermal cross-talk problems are eliminated by providing heat shield members in the space between each of the heater elements. The heat shield members include metal fingers attached to either the common heater electrode or one of the control electrodes. It is disclosed the heat shield members enhance flow of heat into the substrate to thereby minimize thermal cross-talk among adjacent channels.
U.S. Pat. No. 5,113,220 to Kwak entitled Drum Cartridge For Electrophotographic Apparatus With Two-Piece Protected Shutter Covering The Drum, discloses a drum cartridge with a protective cover for an electrophotographic apparatus. The protective cover consists of upper and lower covers separately formed from each other, and the upper cover is operable to be opened and closed by a first gear pivoting around a drum shaft of a photosensitive drum. The lower cover is operable to be opened and closed by a connecting rod coupled to a second gear in mesh with the first gear, and has a driving pin driven by external force. According to the construction, the protective cover is automatically opened and closed by mounting and separating the drum cartridge, and capable of making the exposed area of a photosensitive drum be wide in an open position and protecting the photosensitive drum in a closed position.
U.S. Pat. No. 5,266,999 to Yashiro entitled Process Cartridge And Image Forming Apparatus For Use With The Same, discloses a process cartridge removably mountable within an image forming system including an image bearing member, process means acting on the image bearing member, a protection member shiftable between a protection position where the protection member protects the image bearing member and a retracted position where the protection member is retracted from the protection position, and abutment means formed on a surface of the protection member which can face the image bearing member, wherein the abutment means is adapted to be abutted against a non-image forming area of the image bearing member.
U.S. Pat. No. 5,469,242 to Yu, et al. entitled Corona Generating Device Having A Heated Shield, disclose a corona generating device of the type having a conductive shield partially surrounding a corona discharge electrode that is provided with a heating element. It is disclosed the heating element raises the surface temperature of the conductive shield to reduce or eliminate the adsorption of corona effluents and thereby minimize or prevent copy quality defects.
U.S. Pat. No. 5,589,918 to Oshida, et al. entitled Process Cartridge, Assembling Method Therefor And Electrophotographic Apparatus, disclose a process cartridge detachably mountable to an image forming apparatus, wherein the image forming apparatus light emitting means and light receiving means cooperative with the light emitting means to detect the amount of toner in a part of the process cartridge. The process cartridge includes an electrophotographic photosensitive member; process means actable on the electrophotographic photosensitive member; a toner container, adapted for being mounted in the part, for containing the toner to be used for developing a latent image formed in the electrophotographic photosensitive member; a light transmitting member, provided in the toner container, for transmitting light emitted form the light emitting means to permit detection of the amount of the toner in the toner container when the process cartridge is mounted to a main assembly of the image forming apparatus; a cover member movable between a protecting position for protecting the electrophotographic photosensitive member and a retracted position wherein the cover is retracted from the covering position, wherein upon movement of the cover member from the protecting position to the retracted position when the process cartridge is mounted to the main assembly, the cover member is retracted toward the toner container beyond a position of the light transmitting member.
U.S. Pat. No. 5,794,102 to Coffey, et al. entitled Toner Cartridge With Heat Shield Shutter, disclose a toner cartridge having a single molded element, molded of polystyrene, which is heat sensitive. The molded element forms front handles and a cleaner chamber mounts a photoconductor drum. A toner hopper is located generally under the handles. A developer roller receives toner from the hopper and applies it to the photoconductor drum. A lower shutter of polycarbonate, which is heat resistant, is mounted on actuating links. It is disclosed when the cartridge is installed in the printer the actuating links are moved to rotate the shutter to a position covering the lower surface of the cleaner chamber, where it serves as an effective heat shield protecting the cleaner from fixing heat of the printer.